There is disclosed as a prior art pertaining to the related technical field a gas (deuterium) discharge tube in Japanese Patent Laid-Open (Tokukai) No. H06-310101 publication. In a gas (deuterium) discharge tube described in this publication, there are arranged two metal partition walls within the discharge path between an anode and a cathode, wherein each of the metal partition walls is provided with small holes, whereby the discharge path is caused to be narrowed. As a result, it is made possible to obtain light with a high luminance by means of the small holes on the discharge path. Further, provision of three or more metal partition walls could lead to a further higher luminance. The smaller holes are made, the higher luminance of light there can be obtained.